The present disclosure relates to turbomachinery, and, more specifically, to methods and systems for detecting and locating turbine component surface features, such as cooling apertures, during repair of turbine components.
At least some known turbomachines, such as gas turbines, include surface features such as cooling air apertures that are defined on surfaces of turbine nozzles, rotor blade airfoils, and/or shrouds. Turbine nozzles, rotor blade airfoils, and/or shrouds typically include a substrate over which a coating is applied. During fabrication, after the coating has been applied, surface features such as cooling apertures are defined, for example by drilling through the coating and into, and/or through, the substrate. When a turbine component is repaired, the coating is removed. Cooling apertures previously drilled into the substrate remain after the substrate has been repaired. However, challenges may be presented when a stripped turbine component is being repaired and recoated with a corrosion and/or heat-resistant coating, wherein subsequent recoating of the turbine component may undesirably obscure surface features located on the turbine component. Restoration of cooling apertures to their original geometries, and removal of any excess coating debris obstructing or blocking the cooling apertures, are important to a successful and complete repair of the turbine component.
At least some known repair methods involve visually scanning a component, after the coating has been removed, to record locations of cooling apertures as a set of data points. After the coating has been reapplied, cooling apertures that have been obscured and/or covered over by the coating are cleared via a clearing device. The clearing device may be a device such as, but not limited to, a laser, a water jet, an electrical discharge machining device (“EDM”), an electrochemical machining (“ECM”) device, a mechanical removal device (such as, but not limited to, a drill or reamer), an ultrasonic device, and/or a grit blasting device, coupled to a robotic arm or similar device. The movements of the robotic arm are controlled by a programmable controller that relies upon the previously-recorded data points to precisely position the clearing device. Without a verified initial starting point, however, the programmable controller may not be able to position the clearing device with sufficient precision to clear the cooling apertures without removing more of the reapplied coating than is necessary to clear the cooling apertures.
As an alternative, at least some repair methods may involve the placement of elongated plugs in the cooling apertures prior to reapplication of the coating layers, such that the plugs extend above the reapplied coating layers to indicate the locations of the cooling apertures. However, such elongated plugs may interfere with the reapplication of the coating. Moreover, because of the number of cooling apertures that may be present on a single turbine component, placing a plug in each cooling aperture may represent a time-consuming effort.